ABSTRACT Atherosclerosis, the major cause of cardiovascular disease (CVD), leads to heart attacks, strokes, and peripheral vascular diseases. Although tremendous advance in the research and clinical practice has been made over the past decades, CVD remains the leading cause of morbidity and mortality in the world. Any new therapeutic approaches for atherosclerosis would be a highly significant advance in the treatment of the epidemic prevalence of CVD. Endothelial cells (EC) dysfunction is a hallmark and initial step of atherosclerosis. Transmembrane 6 superfamily 2 (TM6SF2) is a transmembrane protein mainly localized at the endoplasmic reticulum (ER). Using exome-wide association studies, we were the first to identify a coding variant (E167K) in the human TM6SF2 gene exhibiting negative correlation with total cholesterol and myocardial infarction, defining this as a resilience variant. Although we and others have clearly established the reverse association of TM6SF2 E167K variant with cardiovascular events in human genetic studies, the overall function and detailed mechanism of TM6SF2 in the cardiovascular system are still largely unknown. We herein established for the first time that TM6SF2 induces EC inflammation and ER stress and the TM6SF2 E167K allele attenuates the effects of TM6SF2 in ECs. We found that IRE1, a major player in ER stress, is activated by TM6SF2 in primary human ECs. Here we hypothesize that endothelial TM6SF2 is required for atherosclerosis by activating ER stress and inflammation. In this proposal, we aim to define and characterize the driving role of TM6SF2 in EC inflammation and atherogenesis by systematically implementing both gain- and loss-of-function strategies in vivo and in vitro. Specifically, we will: 1). Define the role of TM6SF2 in endothelial inflammation and ER stress in vitro; 2). Define the role of TM6SF2 in atherosclerosis in vivo. The success of this proposal will provide novel insights into our understanding of a human CVD-relevant gene, TM6SF2, and its cellular function in the vasculature, and will set the basis for development of new approaches to the treatment of CVD.